This application claims the priority of Korean Patent Application Nos. 2003-78040, filed on Nov. 5, 2003 and 2004-44510, filed on Jun. 16, 2004, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a motor, and more particularly, to a motor that can prevent dry friction caused during initial operation and discharge static electricity generated during operation by employing both an air dynamic bearing and a fluid dynamic bearing that uses oil of predetermined viscosity. The present invention also relates to a motor having an improved load support force that can bear the load of a plurality of platters for recording and/or collecting a great amount of information.
2. Description of the Related Art
Recently, hard disk drives (HDDs) are required to have a high capacity as multimedia is increasingly used. In particular, HDDs for servers in which a great amount of information is exchanged and stored have always been required to have a large capacity.
High capacity HDDs can be realized by increasing the recording density of a platter or the number of platters. Low non-repeatable runout (NRRO) is needed for increasing the recording density of a platter. Developing a fluid dynamic bearing, which is substituted for a conventional ball bearing, has achieved considerable success in reducing NRRO.
When only a fluid dynamic bearing is used, however, the viscosity of oil is reduced due to frictional heat generated in the oil during a high speed rotation, thereby decreasing the load support force of the fluid dynamic bearing and deteriorating the performance of a motor.
Meanwhile, an air dynamic bearing does not change product properties, for example, a load support force, due to frictional heat during a high speed rotation, but causes dry friction during initial operation of the motor, thereby obstructing smooth operation.
FIG. 1 is a cross-sectional view of a conventional motor employing an air dynamic bearing 1. When the motor rotates at high speed while maintaining a narrow clearance of several micrometers between a bearing shaft 2 and a sleeve 3 or between both ends of the sleeve 3 and thrust plates 4 and 5, the air dynamic bearing 1 supports a load by forming an air pressure using air introduced into the clearance.
However, since such air does not function as a path through which static electricity generated in a disk of a HDD moves, the static electricity cannot be outwardly discharged.